A laser for dismantling reactors and hardening rails

Laser-based methods are known to be more efficient than traditional approaches for a range of tasks that include dismantling obsolete nuclear reactors, maintaining railroad tracks in good working condition, stimulating chemical reactions, and separating isotopes. Among the attractions of lasers are fewer byproducts, increased reactor cutting speed, enhanced lifetime and capacity of the railway, and the ability to deal with toxic agents without igniting them. Moreover, laser techniques are more effective than other methods in processing radioactive waste. Realizing these capabilities takes a high-power laser with superior optical quality. Acceptable cost and efficiency are additional requirements.

High-power CO₂ lasers are commercially available; however, they are expensive and inefficient, and suffer from deteriorating optical quality as power increases. Alternatives include so-called chemical oxygen-iodine lasers (COILs) and CO lasers. But the COIL, too, is expensive, and there is as yet no industrial prototype. And although NUPEC Corporation, in Tokyo, Japan, has impressively demonstrated a 20kW CO laser for cutting large arrays of steel pipes and plates,¹ the system lacks an optical cable of transferring CO radiation. Furthermore, the laser requires cryogenic components, which adds to its cost.

We propose a CO laser² that dispenses with the need for an optical cable by installing the laser head on the manipulator. Our concept is based on the discharge of stable homogeneous radio frequency (RF) in a supersonic stream and the demonstration of laser generation in a small-scale experimental installation.³ We also devised a computational model for scaling the CO laser with RF discharge. Supersonic expansion makes it possible to obtain the required cryogenic temperatures, and the RF discharge enables us to get optimal parameters for vibrational excitation of CO molecules without an electronic gun.

The reduced ratio of the electric field to gas density (E/N) in a column of gas is stated in the literature.^4,5 With our model, we can calculate the power parameters of the CO laser and optimize them to obtain high values of output power and efficiency. The cost of the laser is kept low through use of standard elements, for example, compressor, RF generator, and power station. Owing to the high density of the gas in front of the supersonic nozzle of the laser head and behind the supersonic diffuser, the closed contour serves as a pipeline that enables flexible positioning of the laser head, for example, on the manipulator. Consequently, no optical cable is needed to transfer laser radiation. A standard compressor can be used because values such as pressure and Mach number can be maintained in a stream that makes it possible to restore pressure upon an input in the compressor up to 1atm.

The model consists of calculations of RF discharge parameters, vibrational kinetic equations, and dynamic gas equations that describe a supersonic stream in the RF discharge zone.

We have considered low-current RF discharge with electron photoemission from the electrode surface and injection of electrons from electrode sheaths in a positive column. A low-current RF discharge is realized when the ratio of the time required for the ions to drift through the sheath and reach the electrode to the period of the RF field is much larger than unity.^6,7 Thus, the electrode sheaths have no time to break up and exist simultaneously at both electrodes.

Plausible applications for the CO laser include dismantling obsolete nuclear reactors and hardening of the surfaces of railway rails. Our next step will be to test the laser in applications involving toxic agents, in processing radioactive waste by extracting ruthenium, and separating isotopes of heavy hydrogen and uranium. These applications can be extended substantially only once the laser is commercially available.